Montréal, Canada
Montréal, Canada
Time filter
Source Type

Delbart C.,CEA DAM Ile-de-France | Delbart C.,University Paris - Sud | Delbart C.,French National Center for Scientific Research | Barbecot F.,GEOTOP | And 6 more authors.
Applied Geochemistry | Year: 2014

Karst aquifers are known for their wide distribution of water transfer velocities. From this observation, a multiple geochemical tracer approach seems to be particularly well suited to provide a significant assessment of groundwater flows, but the choice of adapted tracers is essential. In this study, several common tracers in karst aquifers such as physicochemical parameters, major ions, stable isotopes, and δ13C to more specific tracers such as dating tracers - 14C, 3H, 3H-3He, CFC-12, SF6 and 85Kr, and 39Ar - were used, in a fractured karstic carbonated aquifer located in Burgundy (France). The information carried by each tracer and the best sampling strategy are compared on the basis of geochemical monitoring done during several recharge events and over longer time periods (months to years).This study's results demonstrate that at the seasonal and recharge event time scale, the variability of concentrations is low for most tracers due to the broad spectrum of groundwater mixings. The tracers used traditionally for the study of karst aquifers, i.e., physicochemical parameters and major ions, efficiently describe hydrological processes such as the direct and differed recharge, but require being monitored at short time steps during recharge events to be maximized. From stable isotopes, tritium, and Cl- contents, the proportion of the fast direct recharge by the largest porosity was estimated using a binary mixing model. The use of tracers such as CFC-12, SF6, and 85Kr in karst aquifers provides additional information, notably an estimation of apparent age, but they require good preliminary knowledge of the karst system to interpret the results suitably. The CFC-12 and SF6 methods efficiently determine the apparent age of baseflow, but it is preferable to sample the groundwater during the recharge event. Furthermore, these methods are based on different assumptions such as regional enrichment in atmospheric SF6, excess air, and flow models among others. 85Kr and 39Ar concentrations can potentially provide a more direct estimation of groundwater residence time. Conversely, the 3H-3He method is inefficient in the karst aquifer for dating due to 3He degassing. © 2014 Elsevier Ltd.

Veron A.J.,Aix - Marseille University | Flaux C.,Aix - Marseille University | Marriner N.,University of Franche Comte | Poirier A.,GEOTOP | And 3 more authors.
Quaternary Science Reviews | Year: 2013

Recent multidisciplinary investigations of sediment cores from the ancient marine bay of Alexandria (Egypt) have documented local human activities during the Iron Age (circa 900-1000 B.C.) prior to Alexander the Great's arrival in 331 B.C. (Goiran, 2001; Véron etal., 2006; Stanley etal., 2007, 2010), corroborating the existence of the so-called "Rakhotis" as evoked in previous archaeological literature (Jondet, 1916; Weill, 1919; Chauveau, 1999; Baines, 2003). Lead (Pb) Isotopic Analyses (LIA) from Alexandria Bay indicate a possible anthropogenic imprint as early as circa 2300-2650 (±200) B.C. and, to a lesser extent, 3500-3800 (±170) B.C. (Véron etal., 2006). Here we demonstrate that LIA in sediments from the nearby Maryut Lagoon display isotopic anomalies resulting from the release of contaminant Pb into the Lagoon during the Egyptian Early dynastic (at 2897±187 B.C) and Predynastic (at 3520±145 B.C.) periods that corroborate geochemical data from Alexandria Bay. Pb concentrations in Maryut sediments show enrichments that mirror isotopic findings. The absence of contaminant Pb imprints within the sediments from the nearby Nile Canopic branch confirms that isotopic anomalies found in Alexandria Bay and Maryut Lagoon sediments are local and do not originate from long-distance transport of contaminant Pb associated with Nile suspended material and/or wind-derived aerosols. LIA in Alexandria sediment cores correspond to commonly mined Pb and Cu (copper) ores from Turkey (Black Sea region), Cyprus, Crete and the Oman Gulf. LIA substantiate the use of copper-based relics in the Alexandria region during the Pre and Early dynastic periods, and provide insights into metal trading within the Eastern Mediterranean during the Chalcolithic-Early Bronze Age transition, 6000 years ago. © 2013 Elsevier Ltd.

Dabrio C.J.,Complutense University of Madrid | Zazo C.,CSIC - National Museum of Natural Sciences | Cabero A.,Spanish University for Distance Education (UNED) | Goy J.L.,University of Salamanca | And 7 more authors.
Quaternary Science Reviews | Year: 2011

This paper investigates a series of small-scale, short-lived fluctuations of sea level registered in a prograding barrier spit that grew during the MIS 5e. This interglacial includes three highstands (Zazo et al., 2003) and we focus on the second highstand, of assumed duration ∼10 ± 2 ka, given that U-Th ages do not provide more accurate data. Geometry and 3D architecture of beach facies, and thin-section petrography were used to investigate eight exposed offlapping subunits separated by seven conspicuous erosion surfaces, all interpreted as the result of repeated small-scale fluctuations of sea level.Each subunit records a relatively rapid rise of sea level that generated a gravelly shoreface with algal bioherms and a sandy uppermost shoreface and foreshore where most sand accumulated. A second range of still smaller-scaled oscillations of sea level has been deduced in this phase of sea-level fluctuation from lateral and vertical shifts of the foreshore-plunge-step-uppermost shoreface facies.Eventually, progradation with gently falling sea level took place and foreshore deposits underwent successive vadose cementation and subaerial dissolution, owing to relatively prolonged exposure. Later recovery of sea level re-established the highstand with sea level at approximately the same elevation, and there began deposition of a new subunit. The minimum sea-level variation (fall and subsequent rise) required to generate the observed features is 4 m. The time span available for the whole succession of events, and comparison with the Holocene prograding beach ridge complex in the nearby Roquetas (Almería) were used to calculate the periodicity of events. A millennial-suborbital time scale is suggested for fluctuations separating subunits and a decadal scale for the minor oscillations inside each subunit. © 2010 Elsevier Ltd.

Petit D.,Laboratoire Intercommunal Bruxellois Of Chimie Et Of Bacteriologie | Veron A.,Aix - Marseille University | Flament P.,University of the Littoral Opal Coast | Deboudt K.,University of the Littoral Opal Coast | Poirier A.,GEOTOP
Comptes Rendus - Geoscience | Year: 2015

A review of the transient decline of pollutant lead in the air (PbA) and the blood (PbB) has been conducted in order to assess the relationship between these environmental reservoirs. We have demonstrated that PbA decreased 20 to 100 times more than PbB for the past 30years, suggesting another significant intake besides airborne lead to explain lead accumulated in humans. This trend has also been observed in two blood surveys we have completed in 1976-1978 and 2008-2009 in northern France and Belgium. Nowadays, the mean PbB (1.5-3.5μg/dL) remains at least 100 times higher than the estimated non-contaminated PbB. Lead isotope imprints in blood could help decipher specific contamination cases, and were coherent with the decline of PbA, but could not help discriminate the source of blood lead owing to the lack of source imprints, especially from dietary intakes. Correlations between recent PbB, isotopic imprints and the age of the subjects suggested that lead released from bones has become a significant source of lead in blood. The significant cause for human exposure to lead may have shifted from direct pollutant lead input accumulated in exogenous reservoirs (air and diet) to endogenous lead release from bone tissues consequential to metabolic calcium homeostasis and bone turnover. © 2015 Académie des sciences.

Eynaud F.,University of Bordeaux 1 | Malaize B.,University of Bordeaux 1 | Zaragosi S.,University of Bordeaux 1 | De Vernal A.,GEOTOP | And 8 more authors.
Geophysical Research Letters | Year: 2012

During the late Quaternary, both external and internal forcings have driven major climatic shifts from glacial to interglacial conditions. Nonlinear climatic steps characterized the transitions leading to these extrema, with intermediate excursions particularly well expressed in the dynamics of the Northern Hemisphere cryosphere. Here we document the impact of these dynamics on the north-eastern North Atlantic Ocean, focussing on the 35-10ka interval. Sea-surface salinities have been reconstructed quantitatively based on two independent methods from core MD95-2002, recovered from the northern Bay of Biscay adjacent to the axis of the Manche paleoriver outlet and thus in connection with proximal European ice sheets and glaciers. Quantitative reconstructions deriving from dinocyst and planktonic foraminiferal analyses have been combined within a robust chronology to assess the amplitude and timing of hydrological changes in this region. Our study evidences strong pulsed freshwater discharges which may have impacted the North Atlantic Meridional Overturning Circulation. © 2012. American Geophysical Union. All Rights Reserved.

Ouellet A.,GEOTOP | Ouellet A.,Concordia University at Montréal | Lalonde K.,GEOTOP | Lalonde K.,Concordia University at Montréal | And 8 more authors.
Journal of Geophysical Research: Biogeosciences | Year: 2012

Most natural freshwater lakes are net greenhouse gas (GHG) emitters. Compared to natural systems, human perturbations such as watershed wood harvesting and long-term reservoir impoundment lead to profound alterations of biogeochemical processes involved in the aquatic cycle of carbon (C). We exploited these anthropogenic alterations to describe the C dynamics in five lakes and two reservoirs from the boreal forest through the analysis of dissolved carbon dioxide (CO2), methane (CH4), oxygen (O2), and organic carbon (DOC), as well as total nitrogen and phosphorus. Dissolved and particulate organic matter, forest soil/litter and leachates, as well as dissolved inorganic carbon were analyzed for elemental and stable isotopic compositions (atomic C:N ratios, δ13C org, δ13Cinorg and δ 15Ntot). We found links between the export of terrestrial organic matter (OM) to these systems and the dissolved CO2 and O 2 concentrations in the water column, as well as CO2 fluxes to the atmosphere. All systems were GHG emitters, with greater emissions measured for systems with larger inputs of terrestrial OM. The differences in CO2 concentrations and fluxes appear controlled by bacterial activity in the water column and the sediment. Although we clearly observed differences in the aquatic C cycle between natural and perturbed systems, more work on a larger number of water bodies and encompassing all four seasons should be undertaken to better understand the controls, rates, and spatial as well as temporal variability of GHG emissions, and to make quantitatively meaningful comparisons of GHG emissions (and other key variables) from natural and perturbed systems. © 2012. American Geophysical Union. All Rights Reserved.

Fagel N.,University of Liège | Not C.,GEOTOP | Not C.,University of Tokyo | Gueibe J.,TIME Higher School | And 2 more authors.
Quaternary Science Reviews | Year: 2014

Mineral assemblage, trace element content and Nd and Pb isotope signatures were analysed on the fine fraction (<20μm) of sedimentary records from the Northern Mendeleev Ridge in the Central Arctic Ocean. Our aim was to identify the detrital particle provenance and to interpret the changes over the past ~250ka in the relative contribution of the different source-areas in relation to paleoenvironmental conditions. The clay mineral assemblage and the Nd and Pb isotope signatures depict systematic changes over the Late Quaternary. The bulk mineralogy exhibits increases in the relative contribution of carbonate minerals vs. silicates in interglacial/deglacial intervals. In glacial intervals, the mineral assemblage of the <20μm fraction is characterised by an enrichment in kaolinite, counterbalanced by a decrease in illite. The Nd and Pb isotope signatures of <20μm fraction are interpreted using a three end-member mixing model, involving crustal supplies from North America and Canada, from the Siberian margin and some from volcanic material. A compilation of geochemical signatures of geological terraines surrounding the Arctic Ocean allowed each end-member to be assigned a representative signature, averaging the signal of the eroded terraines. The Suspended Particulate Matter (SPM) of the MacKenzie River represents an average signature of the sedimentary supplies delivered from the North American platform and Canadian margin. The SPM of the Lena River reflects the mean sedimentary signature of the Siberian platform. The Okhotsh-Chukotka province from the Eastern border of Siberia is identified as the most probable volcanic source. Late Quaternary evolution of the estimated relative contribution of the three end-members confirms that the sediment provenances in the Central Arctic Ocean remain close to the current conditions during past interglacials/deglacials MIS1-3, MIS5/TII and MIS7/TIII. In contrast, glacial conditions (MIS4 and MIS6) record minimum supplies from the American margin, associated with increased volcanic contribution, to the Mendeleev Ridge core location suggesting a different sea-ice circulation associated with a low sea-level and reduced shelf area. © 2014 Elsevier Ltd.

Loading GEOTOP collaborators
Loading GEOTOP collaborators